[单选题]
X-rays of wavelength 0.20 nmsx*(6qf9 h9wl6 vye pb a4nnpdhc4)qz2 0lsn 0p re scattered by a metal. The wavelength shift is oh n0l4d0p)p n4qnc 2szbserved to be $2.1 \times 10^{-12} \; m$ at a certain scattering angle measured relative to the incoming X-ray. What is the scattering angle?
A. $20^{\circ}$
B. $40^{\circ}$
C. $60^{\circ}$
D. $80^{\circ}$
